The rapid proliferation of the red encrusting macroalgal Ramicrusta in the Caribbean is raising concerns about its ecological impacts, particularly its ability to outcompete foundational benthic species, inhibit invertebrate recruitment, and overgrow living coral colonies, often leading to coral mortality (Eckrich & Engel, 2013; Edmunds et al., 2019). Coral genera exhibit varying levels of susceptibility to Ramicrusta colonization, with Orbicella sp. among the most vulnerable and experiencing high alga overgrowth rates (Hollister et al., 2021; Fig. 1).
Considerable evidence illustrates Ramicrusta’s tendency to interact with and overgrow live corals (Eckrich & Engel, 2013; Ballantine et al., 2016; Edmunds et al., 2019; Hollister et al., 2021), yet there is a disconnect when it comes to understanding the factors contributing to this relationship. Macroalgal growth is typically nutrient-limited, especially in oligotrophic tropical waters (Amato et al., 2016; Strait et al., 2021). Thus, Ramicrusta may be deriving nutrients from the coral itself, fueling these interactions and promoting its own growth.